1. Technical Field
The present invention relates to a printing apparatus which forms an image on a printing surface of a printing medium which is transported in the sub-scanning direction by causing a carriage with a printing unit mounted thereon to move in the main scanning direction.
2. Related Art
An ink jet printing apparatus is a well-known representative example of such a printing apparatus. In the printing apparatus, a printing unit such as a print head discharges ink droplets toward a printing medium surface while moving in a transport direction of the printing medium, that is, the main scanning direction which orthogonally intersects the so-called sub-scanning direction, in a position of being distanced upward from the printing medium surface (the printing surface), and the printing medium is sequentially transported in the sub-scanning direction. In this manner, images, characters and the like are printed onto the printing medium.
In the printing apparatus, there is a case in which wrinkling occurs in the printing medium due to transport shifting during the transporting of the printing medium. In addition, there is a case in which so-called cockling occurs in which the printing medium forms waves due to stretching or the like caused by ink absorption of the printing medium or heating of the printing medium. When these phenomena occur, there is a case in which the printing medium lifts up partially and the print head rubs against or collides with the printing medium surface during a printing operation.
Therefore, in order to suppress such problems, an apparatus disclosed in JP-A-5-262019 (paragraph [0035]) is proposed, for example. The apparatus is provided with a sensor which detects a gap (an interval) between a printing medium and a print head, and when a detection result according to the sensor deviates from a stipulated amount, it is determined that lifting up of the printing medium has occurred and the movement of the carriage is stopped. Accordingly, in the apparatus, rubbing and collision of the print head in relation to the printing medium surface is suppressed.
Incidentally, in order to suppress the rubbing and the collision of the print head, it is important to detect the lifting up of the printing medium. Therefore, in the related art, in order to detect the gap between the printing medium and the print head, the technology disclosed in JP-A-2006-168138 (FIG. 12) is proposed, for example. The apparatus disclosed in JP-A-2006-168138 (FIG. 12) irradiates the printing medium with light, receives the regular reflection light from the printing medium surface using a line sensor, and calculates the distance from the print head to the printing medium, that is, the so-called printing medium distance, on the basis of the output from the line sensor.
However, since the printing medium distance is obtained using regular reflection light, there is a case in which the printing medium is inclined according to the surface state of the printing surface, in particular, whether or not the lifting up occurs in the printing medium, the angle of the regular reflection changes, and it is difficult to accurately calculate the printing medium distance. Therefore, when the invention disclosed in JP-A-2006-168138 (FIG. 12) is applied to the apparatus disclosed in JP-A-5-262019 (paragraph [0035]) as the unit which detects the lifting up of the printing medium, there is a possibility that the rubbing and the collision of the print head in relation to the printing medium surface (the printing surface) may not be avoided, or that even when the rubbing and the collision do not occur, the movement of the carriage will be stopped. Accordingly, there is a concern that the effect of suppression of the rubbing or the like is not sufficiently exhibited.